"Oh, no!" Kathryn exclaimed, wide-eyed that she had, even accidentally, insinuated such a thing. "It's just that, sometimes, one of the babies dies naturally. If the other survives, he or she will have a whole soul. If both babies live, sometimes the parents keep them. More often they are given to the Church to raise and protect from magic and evil. Being twins -- with only half a soul -- they're more susceptible, see."
Yes, to her it made complete sense -- but, of course, it was the only thing she'd ever known! To her, it was simply a fact... And, of course, there were families who did kill the twin -- but most in her circle hid the truth so well that Kathryn would never even consider it an option.
She smiled slightly in response to Rhakōnba's desire to wait to marry. "I suppose," she murmured, "If humans were as long-lived as your people, we might be able to wait longer. I should be engaged soon and married within the year. And if I am not married by 25, I'll be considered an old maid, and no one will want to marry me at all." That, she thought, wouldn't be so bad, really... She could retire to a convent -- or at least pretend to.